Concurrent validity of a markerless motion capture system for the assessment of shoulder functional movement

As a markerless motion capture system(MLS),the Microsoft Kinect sensor may be a low-cost and portable option for measuring shoulder joint angles.However,the system's concurrent validity to capture shoulder functional movement is unclear.The purpose of this study was to investigate the concurrent validity of MLS for capturing shoulder kinematics during functional movement by comparing the MLS measures to those of the marker-based motion capture system(MBS).Twenty-five healthy participants were included in this study.Using the Microsoft Kinect sensor as the MLS and Vicon as the MBS,six shoulder functional movements were measured in all three anatomical planes concurrently.The six movements included flexion to max,maximum extension,abduction to 90°,internal rotation at 90°abduction,external rotation at 0°abduction,and maximum horizontal adduction.The shoulder joint kinematics was measured with both systems.The MLS showed a good to excellent correlation(r>0.75)with MBS for abduction to 90°,maximum external rotation at 0°abduction and maximum internal rotation at 90°abduction.The results for maximum extension(r=0.727)and maximum horizontal adduction(r=0.619)showed a moderate to good correlation.For maximum flexion,a poor correlation was observed(r=0.479).The validity of the MLS to measure shoulder kinematics would be acceptable.The system demonstrates potential as a measurement tool of joint motions for a function assessment and rehabilitation purpose.